Wash oranges well. Place whole oranges in a pot and fill about ½ way up with water. Simmer whole oranges (DO NOT CHOP) for about 45 minutes to 1 hour until soft when you touch them but not falling apart, uncovered. Keep an eye on your oranges, if the water level evaporates add a little more water to the bottom of the pan. Drain water and allow oranges to cool. (Alternatively, you can cook your oranges in the microwave on high power for 15 minutes. However, we have had better results with the stove top method) We left our oranges cool the remainder of the time on the refrigerator overnight. (You do not need to let them cool in the refrigerator overnight but you need to get them cool enough to handle and peel. That can be done the same day)
Pre-heat oven to 350-degree F (180 degrees C)
Line your 9-inch baking pan with waxed paper/parchment paper. We used a spring form pan and it seemed to work well. However, a regular 9-inch cake pan is also okay as if you line your pan with the parchment paper. If you leave a little excess parchment paper at the top, you can just lift straight out of the pan. As a precautionary measure sprayed the parchment paper with a little spray oil.
Prepare your oranges. Cut your cooked and cooled oranges in half. Peel your oranges. Keep the peel. Scrap and remove the white pith from the orange peel with a spoon delicately and discard the pith. Remove any seeds from the oranges. Remove any tough sections from the oranges and discard. Chop the flesh of the oranges and the orange peel of the oranges roughly with a knife. Place your cleaned and chopped oranges and orange peel into a food processer and blend until smooth. Alternatively chop finely with your knife. Set aside.
Separate the egg whites from the egg yolks. Place your egg whites in a large bowl and whisk until stiff peaks. We used a blender but you can also do by hand. Add ½ of the granulated sugar mixture gradually while whisking for about 1-2 minutes or until the eggs turn shiny and glossy in color.
In another large bowl. Whisk the egg yolks and the other half of the granulated sugar about 2 minutes until the mixture is light and fluffy in color and thicker in texture. Add the pureed orange mixture and the ground almonds and mix together.
Slowly and gently, fold in the egg white mixture into the egg yolk, orange and almond mixture, just until mixed together. Do NOT beat or mix, but fold as you want to keep this cake light and airy.
Pour the finished cake mixture into your prepared cake pans. Gently smooth over the top with a spatula and top with sliced almonds.
Bake Best Orange Almond Flourless Cake for 20 minutes on the middle rack and then check on her. If your cake starts to get to brown before set then set a loose layer of aluminum foil over the top until finished baking. Reset timer for another 15 minutes and check on your cake. (We have an uneven oven that drives us crazy!!! We always must turn our items that are baking to assure our food bakes evenly on all sides) Your cake will take between 45-55 minutes to cook or until the toothpick comes out clean when placed in the center of the cake. Our cake cooked in about 45 minutes. Every oven is a little different.
Allow your Best Orange Almond Flourless Cake to cool in the pan. Remove from the pan using the sides of the parchment paper and spring form pan functionality. Carefully remove the parchment paper from the cake. Dust with a little powdered sugar before serving and enjoy.
You can store your Best Orange Almond Flourless Cake in a sealed container for a couple of days. We stored our cakes in a one gallon sealable baggie and it stayed super moist and fresh in the refrigerator. We enjoyed it the next day as a sweet breakfast treat with our coffee in the morning.